Aug., 1941
THEHEATCAPACITY OF POTASSIUM DIHYDKOCEN PHOSPIIATE
h. p. 125.6-126.9', nZ0D 1.3940, 65.7% yield based 011 unrecovered butyl trichloroacetate. Treatment of butyl trichloroacetate with acetic acid a t 115" for nine hours in the presence of p-toluenesulfonic acid led to no products of acetolysis. Butyl trichloroacetate was recovered in 93'z yield. A solution of 56 g. of ethyl butyrate, 48 g. of fused potassium acetate and 5 cc. of acetic anhydride in 100 cc. of acetic acid-acetic anhydride was boiled for eight hours. No evidence of ethyl acetate was found. Ethyl butyrate was recovered, 119-120.5", 13% 1.3923, 48.3 g., 867;.
Summary The results of a qualitative study of the effect of structure of the alkyl group on the acetolysis of
[CONTRIBUTION No. 484 FROM
THE
13'37
esters are reported. I n the acid catalyzed acetolysis of esters of benzoic acid, the 1-butyl ester was found to be quite reactive, the i-propyl ester, less reactive, and the ethyl and methyl esters, inert under comparable conditions. In the base-catalyzed acetolysis, a typical aliphatic ester was found to be inert, while butyl trichloroacetate was reactive. These reactions lead to ester interchange by the exchange of the acid parts of the esters. The mechanisms of these reactions are discussed. I,OSANGELES, CALIFORNIA RECEIVED FKBRUARY 12, 1914
RESEARCH LABORATORY OF PHYSICAL CHEMISTRY, MASSACHUSETTS INSTITUTE OF TECHNOLOGY]
The Heat Capacity of Potassium Dihydrogen Phosphate from 15 to 300'K. Anomaly at the Curie Temperature
The
BY C. C. STEPHENSON AND J. G. HOOLEY' Material.-The salt was of c. P. reagent qualThe heat capacity of KHzP04 is of particular interest since this salt has unusual dielectric ity and contained less than 0.03% impurities6 properties a t low temperatures. Busch2 found other than water. The salt was dried over phosthat KHzP04 is similar to Rochelle salt in that it phorus pentoxide and in vacuum; the heat cahas an electric Curie point: below this tempera- pacity measurements in the neighborhood of the ture, the salt is spontaneously polarized along the ice point show the absence of water. The perc-axis. The electric properties of Rochelle salt, centage loss of weight on ignition to KPOI was KHzPO4 and KH?Rs04 are very similar to the 13.29; theoretical, 13.24. The material used for magnetic properties of ferromagnetic siibstance~,~the measurements consisted of small crystals and anomalies in the heat capacities of these sub- approximately 1 X 0.2 X 0.2 mm. stances are to be expected near the Curie points. All measurements were made on a single caloThe recent investigations of the heat capacity rimeter loading of 104.923 g. in vucuo, or 0.7710 of Rochelle salt by Hicks and Hooley4and by Wil- mole. The molecular weight of KHzPOd was taken son5 have shown that any anomalous increase in as 136.09. the heat capacity of this salt a t the Curie points Method.-The apparatus and method of must be less than one per cent. of the total heat measurement have been described p r e v i ~ u s l y . ~ capacity. Professor Hans Mueller called our at- It is of interest that the calorimeter is the same as tention to the fact that KH2P04 should have an that used by Hicks and Hooley4for their measureeasily detectable anomaly a t the Curie point since ments on Rochelle salt. this crystal has a much larger permanent polarizaThe temperatures were measured by means of a tion than Rochelle salt, and a t his suggestion we platinum-rhodium resistance thermometer-heater have measured the heat capacity of this sub- which had been calibrated previously against a , stance. helium gas thermometer.8 The ice-point resistWhile these measurements were being made, a ance of this thermometer was measured during theory of the transition, derived from a considera- this investigation, and no appreciable departure tion of the arrangement of the hydrogen bonds in from the original calibration value was found. the crystal, was proposed. The entropy change At the conclusion of these measurements and predicted from theory is in agreement with the corresponding measurements on KHzAs04, the experimental value reported in this paper. Con- heat capacity of the empty calorimeter was refirmation of the theoretical entropy change has determined. The new measurernyts are somealso been obtained from a later stucly of the transi- what better than the previous ones due to imtions in KHzAs04 and NH4HzP04. provements in the apparatus and are within the limits of accuracy of the older measurements. (1) Royal Society of Canada Fellow. Fresent address, IJniversity of British Columbia, Vancouver, Canada. The resistance thermometer and thermocouple (2) G.Busch, Helw. P h y s . A d a . 11, 269 (1938). readings were taken on a new Wenner potenti(3) For a review of recent work, see H. Miieller, "Annals of the New York Academy of Sciences," XL, 321 (1940). (4) J. F. G. Hicks and J . G. IIooley, Tms JOURNAL. 60, 2!391 (1938).
(S) A. J. C. Wilson, P k y s . Reo., 64, 1103 (3988).
(6) Prof. S. G.Simpson of the Analytical Division of the Chemistry Department, M . I . T . ,kindly performed the quantitative analyses. (7) J. F. G. Hicks, THIS JOWRNAL, 60, 1000 (1038). (8) K. W. M i l e and J. F. G Hicks, i b i d . . I D , loti2 (1037).
'FABLE 1
HEATCAPACITS V F POTASSIUM DIHYDROGEN PHOSPK4TI~ Molecular weight, 136.09: O'C. = 273.19'K. CP,
T,OK. AT 16.14 2.472 18.66 2.652 22..i0 2.337 25.28 2.452 28.75 3.67:3 .32. 58 ; j ,213 1 :15,97 :$,:I54 *'%I. 7.5 1, 37;3 14.0C 4.872 48.58 4.404 53.24 4.934 57.09 4.463 60.66 2.678 62.92 1.814 64.28 0.797 65.02 ,626 65.76 .769 66.65 ,905 68.09 1.932 70.66 3.179 74.01 :{. 479 77.92 4.274 83.57 4.036 88.45 5.294 92.52 4.967 93.59 4 . 9 6 3 97.36 4.681 102.18 4.944 107.28 5.157 109.29 5.109 110.69 3.632 112.13 4.435 118.29 2.819 113.98 2.449 11.5.66 1.77:
